1. Field of the Invention
The present invention relates generally to directional control systems for drilling apparatus, and more particularly, but not by way of limitation, to directional control systems particularly suited for controlling a substantially horizontally oriented drill shaft and bit.
2. Brief Description of the Prior Art
Horizontal drilling generally requires three essential features: first, a drill; second, a means of forcing the drill into the ground; and third, a means of controlling the drill during its underground operation. The guidance systems used for controlling the underground operation of a drill generally comprise two types. The first type includes surface generated signals and means for conveying the surface generated signals to the horizontal drill. The second type includes underground sensing means provided in the drill for sensing its position and controlling its position in response to said sensed signals.
With either of the above mentioned types of control systems, a deflection device is utilized to deflect the drill in the desired direction in response to the control signals.
One particularly significant advance in such deflection devices is shown in U.S. Pat. No. 3,888,319 to Bourne, Jr., et al., assigned to the assignee of the present invention. The Bourne, Jr., et al. device includes a roll control mechanism in combination with a deflection device. The roll control mechanism comprises a unit which is actuated by pistons which operate on a ratchet assembly. The ratchet assembly provides a means of transmitting the movement of the roll control mechanism to the outside body of the drill. The deflection unit is mounted near the drill bit and comprises a single shoe which is forced against the drill hole wall in any positiion necessary to provide force against the drill, thereby controlling its direction. The same hydraulic system provides both operation of the roll control mechanism and the deflection unit.
The present invention describes an alternative form of deflection device for use with a control system like that of Bourne, Jr., et al., which eliminates the need for a roll control mechanism.
The deflection device of the present invention is similar in some respects to that disclosed in U.S. Pat. No. 3,437,380 to Lawrence, as particularly shown in FIG. 9 thereof. Both Lawrence and the present invention disclose an outer housing, a first deflecting means utilizing hydraulic rams for movement in a first direction relative to the outer housing, and a second deflecting means utilizing hydraulic rams for movement in a second direction relative to the first deflecting means. The first and second directions are perpendicular.
The present invention, however, provides numerous improvements over the rudimentary disclosure of Lawrence. Significantly, the present invention includes first and second guide means which allow movement of the first and second deflecting means in said first and second directions, while preventing rotation about axes parallel to said first and second directions and preventing movement in said second and first directions, relative to said outer housing and said first deflecting means, respectively.